In the field of anterior spinal surgery, a current procedure being performed is called a transcorporeal procedure. This procedure has been recognized as a viable option for addressing pathologies that rest behind the anterior portion of a vertebra known as the vertebral body, also referred to as the “vertebral corpus.” The pathologies addressed by the transcorporeal procedure are generally around or anterior to the spinal cord or other neural anatomy. The creation of a small hole in the bone of the vertebral body is intended to give the surgeon access to pathology and anatomy in the anterior to central portions of the spine. One of the goals of this procedure is to allow a surgeon to reach across bone to locate and treat pathology affecting a patient without performing a fusion of two vertebral bodies.
This general anatomical area where pathologies exist that are addressable by the transcorporeal procedure include the posterior portions of the vertebral body, the posterior portions of the vertebral endplates, the ligament called the posterior longitudinal ligament, the spinal cord and the spinal canal. This general area will be referred to herein as the “greater anterior epidural space” and/or the “greater epidural space.” This area would necessarily include the nerve roots that traverse the spine, the neural foramen of vertebra, the posterior portions of the intervertebral discs and any pathology that occurs in this area as well as the area itself. Thus, for clarity, “the greater epidural space” can be defined as including posteriorly, the area of anatomy beginning with and including the spinal cord and canal with the canal's contents, to the posterior half of a vertebral body.
One of the procedures attempting to address pathologies in the greater epidural space is called a transcorporeal approach. In a transcorporeal approach, the vertebral body is left in place and a small hole is drilled into and through the corpus of the vertebra. Many surgeons refer to the hole as a surgically created vertebral defect. Therefore the word “defect” may be used interchangeably with “hole” or “void” herein. A feature of the transcorporeal approach is the drilling of a small round hole into the vertebral body beginning anteriorly and directed posteriorly creating an exit at the back of the vertebral body. The trajectory of this hole is such that if performed properly the posterior terminus of the hole is adjacent to the pathology being targeted by this procedure. In a transcorporeal approach, it is through this hole that the surgeon performs a procedure that treats a pathology residing behind the vertebra. Therefore, a transcorporeal hole is actually not just a hole but a functional pathway in which a surgeon performs a procedure.
The transcorporeal approach differs from older, more common standards of care and approaches in spinal surgery in that it is not an inter-vertebral procedure. When used as a prefix, “inter” means “between.” Transcorporeal means the procedure does not go between two vertebral bodies; it goes through a single vertebral body. “Intervertebral” is when a surgical procedure goes between two vertebral bodies. In other words, the procedure goes through a space created by removing an intervertebral disc from between two vertebrae. In an intervertebral approach, an intervertebral implant is normally placed against the remaining external aspects of two vertebrae, between the two vertebrae, against what may remain of the external aspect of an inferior endplate of one vertebra and what may remain of the external aspect of a superior endplate of another vertebra. This type of intervertebral approach usually requires an implant to replace the disc.
The goal of a transcorporeal approach is to avoid disrupting the disc as much as possible and does not include fusing two vertebrae together. Therefore, the goals and function of an implant for transcorporeal repair is different than the goals and function of an implant for intervertebral fusion or disc replacement. A surgeon performs a transcorporeal procedure in order to preserve the disc.
A problem with a typical transcorporeal approach has been the extremely limited exposure to the anatomy and pathologies this approach provides the surgeon. As the name implies, and current technique teaches, in order to be trans-corporeal, the body must be left in place or at least mostly in place in order to work through it and then go on to heal after the surgery is complete. The surgeon must necessarily limit his exposure to working through a tiny drill hole. This limitation to the transcorporeal approach has limited the procedure's adoption and success rate, making it entirely impractical on a large clinical scale. Hence, the transcorporeal approaches are only available to a limited number of patients with very limited pathologies.
Another problem with a typical transcorporeal approach is that if the hole drilled into a vertebral corpus is large enough to provide the significant access most pathologies require, the corpus will not be able to naturally fill the defect back with bone, as it will if the drill hole is kept small. A hole too large for bone to naturally grow back into, ends up leaving the patient with the potential of a vertebral body collapse, fracture, or any of a series of negative long term outcomes. If the hole created is small enough to grow back naturally as part of the body's normal healing pattern, the surgeon is not provided enough space to perform most of the surgical procedures necessary to treat the most common pathologies.
Thus, there is a need for providing an implant that may be used for repairing a substantial defect created in the performance of a transcorporeal surgical procedure. In order to fill the need, the implant must be capable of allowing for the repair of significantly larger and/or more variable defects that may be created in the course of performing a transcorporeal procedure.